YouDDL is probably the best YouTube downloader on internet, because you can download videos in any resolution available. You can even download them in HD ( either in .flv format or in MP4). But you need a video player capable of playing these formats, or a video converter, in order to get them in a playable format. It's free: http://www.youddl.com/
And, I am NOT responsible for anything you download by using this method, including copyrighted content. Use it at your own risk !